Bull Demon is a peace of cake, there are two towers, once you enter the white light head to the right and climb the ladder. Kill archers, climb down, wait for demon to appear and run back, climb ladder, and do a plunge attack on bull-demon for massive damage. You have enough time to hit his legs a few times. Run to other tower, repeat.

Or just lure them of the open part of the bridge and let him fall to death, gravity is your friend in this game!